Display device, in particular for cooktops

ABSTRACT

A display device in particular for cooktops is provide that has a glass ceramic with a front side and a back side and a lamp arranged in the area of the back side. The display device further includes an optical compensation filter arranged between the front side and the lamp so as to implement any color impressions easily and inexpensively and in a preselectable manner.

To improve user guidance, cooktops of modern glass ceramic cookingappliances are equipped with signal lamps or 7-segment displays. Thecooktop itself is made of a transparent pigmented glass ceramic panel(substrate), which appears black when viewed from above. The signallamps provide the user with information about the on state of thecooktop and/or individual cooking zones, the regulator position and alsowhether the cooking zone is still hot after being turned off. LED lampsare usually used as the lamp.

The available color spectrum for user information is severely limitedbecause of the pigmentation of the glass ceramic cooktop and the verylimited choice of colored LED displays. The standard is for thesedisplays to appear in red or optionally orange, which is also the resultof the pigmentation of the glass ceramic surface. DE 10 2008 050 263describes the transmission characteristic of a glass ceramic cooktopwhich allows a permeability for blue light at approx. 450 nm inparticular and thus allows an expanded color display capability.Different display options are conceivable on the basis of this glassceramic. The coloration of the displays has also been expanded byexpanding the transmission spectrum into the blue wavelength range.Because of the small number of variously colored LED displays, however,the number of colors visible for the user is still greatly limited evenwith this glass ceramic cooktop. For example, because of thetransmission characteristic of the cooktop, a white LED would beperceived by the user as having a yellowish cast.

The object of the present invention is to provide a display device ofthe type described in the introduction, with which any predeterminablecolor impressions for the user on the front side of the glass ceramiccan be implemented by signal lamps or display units in a simple,inexpensive and robust embodiment.

This object is achieved in a surprisingly simple way by arranging acompensation filter which corresponds to the desired color impression inthe form of a color film or the like between the glass ceramic cooktopand the lamp, such that the shift in the chromaticity coordinate of thelamp due to the filter properties of the glass ceramic is corrected bythe combination of the glass ceramic with such a compensation filter toyield the desired chromaticity coordinate.

Advantageous design variants of the invention are described in thedependent claims.

The present invention is explained in greater detail below withreference to the tables and figures, in which:

Table 1 shows the corner coordinates of fields in the CIE Norm ValentSystem CIE xyY, as shown in FIG. 3;

Table 2 shows the corner coordinates of additional fields in the CIENorm Valent System;

FIG. 1 shows typical transmission spectra of various glass ceramics forcooktops, as shown in FIG. 2;

FIG. 2 shows a diagram of the chromaticity coordinates of the standardillumination E through various glass ceramics in the CIE Norm ValentSystem;

FIG. 3 shows a diagram of the chromaticity coordinates of standardillumination E through a certain glass ceramic D with and without acompensation filter in the CIE Norm Valent System for whitecompensation;

FIG. 4 shows a diagram of chromaticity coordinates of an LED-RGB lamp(RGB gamut) through a certain type D glass ceramic with and without acompensation filter in the CIE Norm Valent System;

FIG. 5 shows a diagram of transmission curves of compensation filters F₁through F₆, optimized for compensation of the standard light source Eand the type D glass ceramic;

FIG. 6 shows the y tristimulus and the Y values of filters F₁ through F₆according to FIG. 6;

FIG. 7 shows the chromaticity coordinates of a blue LED and of a whiteLED with a blue filter, as observed directly and as observed through aglass ceramic of the Ceran Hightrans® eco type,

FIG. 8 shows brightness spectra of the blue LED and of the white LEDaccording to FIG. 7, as seen through Ceran Hightrans® eco, and

FIG. 9 shows a display device, in particular for cooktops having a glassceramic body 10, in particular a glass ceramic panel, forming a glassceramic front side 12 and a glass ceramic back side 14, and having alamp 16 arranged in the area of the glass ceramic back side,characterized in that an optical compensation filter 18 is arrangedbetween the glass ceramic cooktop 10 and the lamp 16.

The total transmission of the substrate τ_(ges)(λ) [ges=total] iscomprised of the transmissions of the glass ceramic τ_(GK)(λ) [GK=glassceramic] and of the compensation filter τ_(KF)(λ) [KF=compensationfilter] (eq. 1). The intensity distribution i_(LE)(λ) of the lightingelement is shifted through the total transmission spectra τ_(ges)(λ) tothe intensity distribution i_(A)(λ) of the display (eq. 2), as perceivedby an observer on the display side (eq. 2).τ_(ges)(λ)=τ_(KF)(λ)·τ_(A)(λ)   eq. 1i_(A)(λ)=τ_(ges)(λ)·i_(LE)(λ)   eq. 2

The associated shift in the chromaticity coordinate can be representedin the CIE Norm Valent System CIExyY (CIE—Commision internationale del'éclaireage [International Commission on Illumination]). (For thefollowing description and the examples, the 1931 CIExyY version with a2° observer will be used in the present patent specification.) The humaneye is not a spectrally continuous light sensor but instead is composedof color receptors for limited red, green and blue spectral regions.Accordingly, the sensory perception of the L, M and K cones is similarwith sensitivities in the red, green and blue spectra of light. Based ontest series with test subjects, tristimulus functions x, y, z and theirintegrals X, Y, Z, have been defined in the CIE formalism; these canrepresent the entire color space that can be perceived by our eyes as atriplet of artificial primary colors through their combination. In thissystem, the x and z functions only correspond approximately to the L andK cone sensitivities. The y function is constructed to simulate thebrightness perception during the day and corresponds almost to the Mcone sensitivity. With eq. 3 and eq. 4, the perceived chromaticitycoordinate is clearly described by the standardized values x and y, andY is a measure of brightness. The CIExyY formalism describes primarylight sources, optionally shining through absorbent media, whose lightspectrum striking the eye is transformed into the standardized X, Y, ZCIE coordinates which then describe the chromaticity coordinate and thebrightness of the primary light source,

$\begin{matrix}{{A = {\frac{1}{N}{\int{{{\overset{\_}{a}(\lambda)} \cdot {\tau(\lambda)} \cdot {i(\lambda)} \cdot d}\;\lambda\mspace{14mu}{with}}}}}{{A = X},Y,{{Z\mspace{14mu}{and}\mspace{14mu}\overset{\_}{a}} = \overset{\_}{x}},\overset{\_}{y},{\overset{\_}{z}\mspace{14mu}{with}}}{N = {\int{{{\overset{\_}{y}(\lambda)} \cdot {i(\lambda)} \cdot d}\;\lambda}}}} & {{eq}.\mspace{14mu} 3} \\{{x = \frac{X}{S}},{y = \frac{Y}{S}},{z = {{1 - x - {y\mspace{14mu}{with}\mspace{14mu} S}} = {X + Y + Z}}}} & {{eq}.\mspace{14mu} 4}\end{matrix}$

The prerequisite for reaching a desired display chromaticity coordinatein the red to blue spectral range for an observer by means of acompensation filter and by means of a preferably standard commercial andinexpensive display lighting element is minimal transmission values ofthe substrate in the spectral range of all three L, M, K cones, forexample, all three x, y, z CIE primary spectra. FIG. 1 shows typicaltransmission spectra represented by different types (classes) of glassceramic. These include type A glass ceramic pigmented with vanadium (V),which is currently the most widely used glass ceramic (for example,CERAN SUPREMA®, CERAN HIGHTRANS®, KeraBlack®), glass ceramics withpigmentation by Co, Fe, Ni (type B, for example, CERAN COLOR®), by V, Asand Fe (type C, China), by V, Fe (type D, for example, CERAN HIGHTRANSeco®, as described in DE 10 2008 050 263. The composition of these glassceramics is herewith made part of the disclosure content of the presentspecification through this reference. This also includes those withpigmentation by Ti³⁺ by means of reductive reformation (for example, ZnSreformation), i.e., type E.

Creating sufficiently light color impressions in the blue to redspectral range through the glass ceramic on the display side, formed bythe glass ceramic front side, using conventional commercial lamps (forexample, LEDs) requires glass ceramics having an average transmissionof >0.2%, preferably >0.4%, having a spectral range of 420-500 nm,500-620 nm and 550-640 nm. As shown in FIG. 1, this condition is met bythe more recent glass ceramic classes D and E, and, with somerestriction, also class C. Class A glass ceramic, which was previouslyvery popular, does not meet this condition. With this glass ceramic,shifts in the chromaticity coordinate over the entire visible spectralrange such as those accomplished according to the present invention areimpossible with conventional lamps and filters, and in particular thereis also no white compensation. On the other hand, the spectraltransmission must not be too high to prevent insight into the internalstructure of the cooktop fields and to represent an aestheticallypreferred nontransparent cooktop surface that is uniform in color and todo so without any additional aids such as opaque coatings on the bottomside. In the present case, this maximum transmission of the glassceramic body is defined as being <40%, preferably <25% at 400 nm to 700nm, and in addition is between 450 and 600 nm with an average of <4%. AsFIG. 1 shows clearly, this second condition is satisfied by all theglass ceramic classes shown here, except for class C, which appears inpractice to be transparent, to prevent insight into the interior of acooktop. Another condition, i.e., a third condition, is derived from thefeasibility of a color shift to a white color impression of a commerciallamp through a glass ceramic cooktop and a compensation filter that isnot too expensive. To this end, the difference in transmission in thethree spectral ranges of perception must not be too great. This isillustrated in FIG. 3. The chromaticity coordinates of the normalillumination through glass ceramics according to the present inventionshould lie within a limit curve G1, preferably a limit curve G2. Table 2shows the corner coordinates with the limit curves G1 and G2.

If an observer perceives a light stimulus consisting of two lightsignals, which are situated side by side in space but do not appearresolved in space to the human eye and which are described by theintensity distribution of the light elements and by filtertransmissions, then the perceived sensory perception is added uplinearly (eq. 5) and the cursory chromaticity coordinate (x, y) lies ona straight line between the chromaticity coordinates (x₁, y₁) and (x₂,y₂) of the two light signals (eq. 6) in the CIExyY chromaticity diagram.In the specific case of equal intensities (eq. 7), (x, y) lies at thecenter between the chromaticity coordinates of the two light signals(eq. 8).

$\begin{matrix}{A = {{\frac{1}{N}{\int{{{\overset{\_}{a}(\lambda)} \cdot \left( {{{\tau_{1}(\lambda)} \cdot {i_{1}(\lambda)}} + {{\tau_{2}(\lambda)} \cdot {i_{2}(\lambda)}}} \right)}\mspace{14mu}\ldots\mspace{14mu} d\;\lambda}}} = {{A_{1}\left( {\tau_{1},{k_{1}i}} \right)} + {A_{1}\left( {\tau_{2},{k_{2}i}} \right)}}}} & {{Eq}.\mspace{14mu} 5}\end{matrix}$

with i₁=k₁·i, i₂=k₂·i, k₁+k₂=1x=k₁x₁+k₂x₂   Eq. 6

with x_(i)=f(τ_(i), i), corresponding to y, z.k₁=k₂=1/2   Eq. 7

$\begin{matrix}{{x = \frac{x_{1} + x_{2}}{2}},{y = \frac{y_{1} + y_{2}}{2}},{z = {\frac{z_{1} + z_{2}}{2} = {1 - x - {y.}}}}} & {{Eq}.\mspace{14mu} 8}\end{matrix}$

This linear relationship is also known from color diagrams of imagedisplays, such as CRT or LCD monitors, for example, in which possibleperceptible chromaticity coordinates in the CIExyY diagram lie in atriangle between the chromaticity coordinates of the three primarycolors of the display device, which is usually an RGB color space or ina color polygon with more than three primary colors, where thechromaticity coordinate is calculated from the linear combination ofthree or more primary intensities according to (eq. 6).

In the application of two filters arranged one after the other accordingto the invention, a substrate (for example, a glass ceramic) and acompensation filter, the relationship is no longer linear, asillustrated by eq. 9 in comparison with eq. 5. For example, thetransmission spectra of the glass ceramic τ_(GK)(λ) and of thecompensation filter τ_(KF)(λ) may be used in eq. 9 for τ₁(λ) and τ₂(λ)from eq. 1, for example.

$\begin{matrix}{A_{12} = {\frac{1}{N}{\int{{{\overset{\_}{a}(\lambda)} \cdot {\tau_{1}(\lambda)} \cdot {\tau_{2}(\lambda)} \cdot {i(\lambda)}}\mspace{14mu}\ldots\mspace{14mu} d\;\lambda}}}} & {{Eq}.\mspace{14mu} 9}\end{matrix}$

The chromaticity coordinate of the light element through the filtersarranged one after the other is no longer necessarily on a straight linebetween the chromaticity coordinates of the light element through theindividual filters. Conversely, this leads to the phenomenon that thesame shared chromaticity coordinate of a light element through a glassceramic, which has been compensated according to the invention, can beachieved with different compensation filters, such that the chromaticitycoordinate of the light element through the individual compensationfilters need not be identical, depending on the spectral distribution.FIG. 3 shows the chromaticity coordinates of normal light individuallythrough a glass ceramic of type D and individually through differentcompensation filters F1-F5, each of which makes the standard lightappear at the same overall chromaticity coordinate when arranged incombination with the glass ceramic one after the other. In the exampleshown here the color filters are designed so that the overallchromaticity coordinate for the observer is at the achromatic point E(gray point or white point E).

With a color filter according to the invention, it is thus possible, asalready described, to again compensate for the shift in the originalchromaticity coordinate of the lamp through the pigmented substrate, andspecifically to yield a white chromaticity coordinate. A furtherapplication according to the invention is to shift the chromaticitycoordinate of the lamp on the display side of the substrate to a desiredchromaticity coordinate, which is different from the originalchromaticity coordinate of the lamp. The combined shifts in thechromaticity coordinate due to the substrate and the filter do notcompensate one another here as intended. It is thus possible to generatea chromaticity coordinate that cannot be represented by the availablefixed wavelengths of commercial LEDs, for example, a chromaticitycoordinate that is located between a yellow LED and an orange LED. Thisis advantageous in identification, differentiation and marketing ofproduct lines, for example. In addition, lighting elements can beconstructed uniformly and thus with a cost advantage using a variety oflamps that are not monochromatic but instead are colored lamps whichemit over a broad spectral range (for example, white LEDs, fluorescenttubes). By using different color filters according to the invention,different chromaticity coordinates for different product lines or thesame chromaticity coordinates of one product line may be created incombination with substrates of different colors. Chromaticity coordinateshifts and compensations can be used in particular for lamps of a broadband spectrally, such as white LEDs, fluorescent tubes or mixed colorsof combined single-color LEDs, for example, RGB LEDs. Single-color andalmost monochromatic lamps, for example, red, blue and green LEDs, whenused as a single color, do not usually experience any marked shift inchromaticity coordinate due to filters.

Compensating the chromaticity coordinate of a lamp toward whiteaccording to the present invention does not mean hitting precisely theachromatic point E. Instead the eye tolerates a wide chromaticitycoordinate range as a white impression. This also depends on thechromaticity coordinates of the surrounding surfaces such as a reddishblack cooktop surface, among other things. Thus the chromaticitycoordinate of the standard light source E is still perceived as whitethrough a filter F6 and the type D glass ceramic (see FIG. 3) in theenvironment of the cooktop, although it is already perceived asdefinitely reddish in a direct comparison with the chromaticitycoordinate E. Therefore the goal according to the invention for whitecompensation of a lamp of any color is to achieve a chromaticitycoordinate which is within the limits of the white range W1, preferablythe white range W2. The white range W2 surrounds the white fields 1A, .. . , 1D, . . . , 8D, which are defined in ANSI (ANSI binning) and aretypically used by LED manufacturers to characterize the chromaticitycoordinates of their white LEDs. This range corresponds to colortemperatures of 2580K to 7040K (CCT, color correlated temperature), inaccordance with the white impression from cold white to warm white. Thecorner points of the white areas W1 and W2 in FIG. 3, which are definedaccording to the invention, are listed in Table 1.

According to the present invention, the chromaticity coordinatecompensation is not limited to the exemplary filters F1-F5 according toFIG. 5 or the standard light source E. In one application, commerciallyavailable and inexpensive lamps, for example, white LEDs are preferablyused. Lamps of other colors that are not monochromatic, for example,fluorescent tubes or also for example, a combination of red, green andblue LEDs (RGB lamps) which are set at a fixed chromaticity coordinateas background lighting of LCD displays, for example, or which control acolor display on a screen may also be used for compensation by means ofsuitably designed compensation filters on the display side of the cookfield to the original chromaticity coordinate of the lamps orspecifically to generate a white color impression or any other colorimpression.

FIG. 4 shows one example of a correction of an RGB lamp. An RGB lampspans a triangular color space (gamut) between the LED CIExyYchromaticity coordinates which can be represented in the CIExyY colorspace. When observed through a type D glass ceramic, this gamut isshifted toward the red but then the gamut is shifted back by theadditional filter F5 to almost coincide with the original gamut betweenthe LEDs (without glass ceramic and compensation filter). Accordingly,the white point that is set for the RGB lamp (standard light D65 here,for example) when observed through the glass ceramic is shifted towardthe red and again is shifted back to almost correspond with the originalchromaticity coordinate by means of the filter F5. This correction ofthe white point is not exact here because the filter F5 has beenoptimized for a standard light E, and nonlinearities with the spectra ofthe LEDs also play a role (cf. eq. 9).

Filters with a high brightness of the light passing through areadvantageous in general. Since the brightness impression of the humaneye is scaled with the green spectrum and/or the green tristimulusfunction, such filters which have the highest possible transmission inthe green spectral range are preferred according to the invention. Thisis manifested in the fact that the brightness of these in transmissionthrough the filter reaches almost Y=100 with a light source (Y=100).

It has been found that the filters F1-F6 discussed here for chromaticitycoordinate compensation of the standard light source E beneath a type Dglass ceramic will transmit almost uniformly beneath a green wavelength(high-pass frequency filter), for example, filters F4-F6 in FIG. 5 areadvantageous in comparison with those in the brightness impression whichhave a high transmission only in the limited blue and green spectralranges in a targeted manner, for example, filters F1-F3 in FIG. 5.According to the invention, compensation filters with Y>10 (based onstandard light E), preferably Y>40 (based on standard light E) areadvantageous for white point compensation under type D glass ceramics ofwhite lamps. FIG. 6 shows the integrative Y values of the filters F1-F6under the green tristimulus function.

This rule, i.e., a high transmission in the green range, applies ingeneral for combinations of any lamps and filters.

The compensation filter F1 here is a special solution in which itstransmission T_(KF) and the transmission T_(GK) of the pigmented glassceramic cooktop are compensated to a constant value T_(E) which is notdependent on the wavelength (eq. 10). The intensity spectrum I_(LE)(λ)of the lamp is then weakened by a constant value T_(E) to the intensityspectrum I_(A) which appears on the display side (eq. 11). However, thestandard light source E achieves a brightness value of only Y<1 throughthe filter F1.τ_(E)=τ_(KF)(λ)·τ_(GK)(λ)=konst.   eq. 10i_(A0)(λ)=τ_(E)·i_(LE)(λ)   eq. 11konst.=const.

Color filter films must be transparent enough for this use ascompensation filters and must be thermally stable. The compensationfilter F6 is an example of a color filter that is availablecommercially. This film CT113 no. 11383 from the company ASLAN has verygood results in this regard and has thermal stability up to 80° C. Filmsfrom the company Lee or Q-Max have an increased thermal stability up to185° C. and are therefore preferred for use here.

According to the invention, chromaticity coordinate compensation is notlimited to a white chromaticity coordinate. Any desired chromaticitycoordinate may be adjusted with a corresponding compensation filter, forexample, brand-specific colors for displays or company logos ordifferent chromaticity coordinates for user-friendly differentiation ofwarnings, instructions or user aids or different chromaticitycoordinates for different power levels on cooktops. This may be used ina variety of examples which serve to facilitate user guidance, statusdisplays or various ambients of decorative lighting.

In addition, it has been found that commercial colored LEDs, inparticular those in the blue or red color spectrum, are visible withonly restricted brightness when observed through variously pigmentedglass ceramics or other transparent pigmented materials. This is due tothe fact that the human eye has only a low brightness perception in theblue and red spectral ranges in contrast with the green spectral range.Experience has shown that a blue display, for example, can also becreated by means of a white lamp, in particular a white LED, and a bluecolor filter which has a lower color saturation in comparison with ablue LED but advantageously has a much higher brightness. This isillustrated in FIG. 7 in the CIExyY diagram (2° observer) withchromaticity coordinates (x, y) calculated according to eq. 4. Thechromaticity coordinate of a blue 470 nm LED (LED [470 (25)]) issituated close to the trichromacy curve T (square gray symbol, colorsaturation=0.98). The chromaticity coordinate of a white display(CCT=8144) (7-segment LED, opto-devices model OS39D3BWWA), black circle,and this white light through a CERAN HIGHTRANS® eco sample with a blacktriangular symbol is represented likewise. Chromaticity coordinates nearthe trichromacy curve convince us of a high color saturation whilechromaticity coordinates on an imaginary line approaching the neutralpoint (x=0.33, y=0.33) (standard light E—see FIG. 2) have an even lowercolor saturation, the closer they are to the neutral point. As anexample here, the chromaticity coordinate of this aforementioned whitedisplay is shown with a blue compensation filter in the form of a bluecolor compensation film (EURO filter no. 132, “medium blue”), i.e., inone case, the chromaticity coordinate of the light through the film 132(round gray symbol) and the chromaticity coordinate of this white lightthrough the film and a CERAN HIGHTRANS® eco sample (triangular graysymbol, color saturation=0.72). The resulting chromaticity coordinate ofthe CERAN HIGHTRANS® eco sample is almost on an imaginary line 470 nmLED—neutral point (gray square symbol—standard light E). All the pointson this line have the same hue but the color impression appears brightertoward the neutral point (declining color saturation). This whitedisplay with a blue color film creates the same hue in comparison withthe blue LED display but does so with a brighter color impressionthrough the CERAN HIGHTRANS® eco sample. This chromaticity coordinatehas approximately the same limit wavelength as the spectrally purer blueLED close to the trichromacy curve. The greater brightness is explainedby the additional components in the emission spectrum, in particular thegreen components, for which the human eye has a greater sensitivity incomparison with the almost monochromatic blue emission spectrum of ablue LED. This is shown clearly in FIG. 8 on the basis of brightnessspectra. The brightness spectra are the wavelength-dependent functionbelow the integral in eq. 9, multiplication of the transmission spectra,of the light spectrum and of the V(λ) curve. The V(λ) curve describesthe brightness perception of the human eye. The brightness spectra ofthe blue 470 nm LED mentioned above and the white LED display with bluecompensation film (EURO filter no. 132), both observed through CERANHIGHTRANS® eco, are shown as an example. The area under the curvesdescribes the perceived brightness. At approximately the same intensityin the blue spectral range (470 nm), the spectrum of the white displaywith the blue filter (filter that filters the blue light components outof the spectrum of visible light) has an additional component in thegreen (and red) spectral range which creates the greater brightnessimpression. This application according to the invention is not limitedto the blue spectral range. It is possible with this method to implementdisplays with all spectral colors, advantageously creating chromaticitycoordinates that appear brighter or even creating desired chromaticitycoordinates having a lower color saturation in comparison with those ofsingle-color LEDs and correcting the shift in chromaticity coordinate ofa pigmented glass ceramic body, for example, in comparison with almostmonochromatic displays with single-color LEDs.

Within the scope of the invention, masking of films is also conceivable.This masking also allows a sharp delineation of the signal field andshielding of stray light as well as a display of characters, symbols orfonts, which are visible for the user when the lighting is on and cannotbe seen by the user when the lighting is off. Even the position of thesemarks/logos cannot be discerned when the lighting is off, so the fine,single-color appearance of the glass ceramic surface is retained for theuser. This effect is known as the “deadfront effect” and is oftendesired by designers because it significantly enhances the cookingappliance in its overall aesthetics. Since the masking is done directlyin the film (for example, through a second suitably printed black film),this system is much more flexible to use than masking printed directlyon the back of the glass ceramic cooktop, for example.

This deadfront effect is possible only with considerable extra effortwith the transparent glass ceramic cooktops known especially in Japan.Because of the high transparency of these cooktops, displays or lampsare visible directly and/or clearly, which is partially perceived asannoying. In contrast with these transparent cooktops, the cooktops withdark pigmentation are also combined with high-performance radiantheating elements, so that the glass ceramic cooktops having radiantheating elements and/or halogen heating elements are definitely upgradedin user guidance with the method proposed here. In addition to thecolored film preferably to be used as proposed here, including theoptional masking, a printed color coating on the bottom side of thecooktop is also conceivable. It is also conceivable to glue the loosefilm to the bottom side of the glass ceramic and/or to glue a maskedfilm to the bottom side of the glass ceramic. Due to the sharpdelineation by means of masking, image definition on the top side ispossible without visually interfering distortion of fine lines andcharacters when using glass ceramic cooktops which usually have a nubbybottom side. This is another definite advantage in comparison with theknown printed masking on a nubby bottom side. Due to the direct printingof the nubby bottom side there is distortion, which can be veryannoying, so that only very large windows and symbols can be displayed.The cooktop is usually 4 mm thick, but in commercial applications, itmay be up to 6 mm thick. To increase the color intensity and/or luminousintensity, it is also conceivable to use cooktops having a reducedthickness of 3 mm, for example.

In addition to the main field of applications for illumination withsingle LEDs or 7-segment displays as shown here, the system is of coursealso suitable for any other light source and form of display; forexample, halogen lamps, glow sticks, fiber optics or fluorescent tubesmay also be used as the light source. In addition to light spots or7-segment displays, bar displays or illuminated labels for identifyingcooking zones or for marking or illumination of larger cooking areas orborders are also conceivable. In addition, chromaticity coordinatecompensation or shifts according to the invention may also be used forbackground lighting of alphanumeric or graphic displays, for example,LCD displays. In addition to the preferred use in glass ceramic cookingappliances, this system may also be used in the panel area of bakingovens or Domino cooking surfaces, including grill plates. For example,fireplace claddings made of glass ceramic are also known. With thesefireplace claddings, illumination with the proposed system to improveuser convenience is also possible. The cooktop may be designed to beflat or curved or to have a complex shape. Gas burners, induction coilsor radiant heating elements and/or halogen heating elements areconceivable as the heating source for the cooking areas.

TABLE 1 W1 W2 X Y X Y 0.3 0.25 0.3068 0.3113 0.26 0.32 0.3028 0.33040.37 0.43 0.3205 0.3481 0.51 0.48 0.3207 0.3462 0.48 0.35 0.3376 0.36160.35 0.3 0.3551 0.376 0.3548 0.3736 0.3736 0.3874 0.4006 0.4044 0.39960.4015 0.4299 0.4165 0.4562 0.426 0.4813 0.4319 0.4593 0.3944 0.41470.3814 0.3889 0.369 0.3898 0.3716 0.367 0.3578 0.3512 0.3465 0.35150.3487 0.3366 0.3369 0.3222 0.3243 0.3221 0.3261

TABLE 2 Limit curve G1 Limit curve G2 X Y X Y 0.71 0.27 0.64 0.28 0.170.02 0.20 0.07 0.12 0.08 0.17 0.09 0.05 0.30 0.10 0.30 0.01 0.60 0.080.56 0.08 0.81 0.12 0.70 0.28 0.70 0.26 0.65 0.71 0.27 0.64 0.28

The invention claimed is:
 1. A display device for cooktops, comprising:a colored glass ceramic panel forming a glass ceramic front side and aglass ceramic back side, the glass ceramic panel having a meantransmission greater than 0.2% for each of the spectral ranges of420-500 nm, 500-620 nm, and 550-640 nm, and the glass ceramic panelhaving a maximum transmission less than 40% in the entire spectral rangeof 400 to 750 700 nm and less than an average of 4% in the entirespectral range of 450 to 600 nm; a lamp arranged in an area of the glassceramic back side, the lamp being either a combination of at least ablue LED, a green LED, and red LED or being a white lamp; and an opticalcompensation filter arranged between the glass ceramic front side andthe lamp with the glass ceramic panel and the compensation filterforming two filters arranged one after another such that a shift in astandard chromaticity coordinate x, y in the CIE Norm Valent SystemCIExyY (CIE: Commision Internationale de l'Eclaireage, 1931, 2°observer) of the lamp due to filter properties of the glass ceramicpanel is corrected by a combination of the glass ceramic panel and thecompensation filter to yield a desired chromaticity coordinate x, y inthe CIE Norm Valent System CIExyY (CIE: Commision Internationale del'Eclaireage, 1931, 2° observer).
 2. The display device according toclaim 1, wherein the mean transmission is greater than 0.4% for each ofthe spectral ranges of 420-500 nm, 500-620 nm, and 550-640 nm.
 3. Thedisplay device according to claim 1, wherein the maximum transmission isless than 25% in the spectral range of 400 to 750 nm.
 4. The displaydevice according to claim 1, wherein the glass ceramic panel causes thestandardized chromaticity coordinate of the lamp to appear on or abovethe limit curve (G1) which is determined by the following coordinates intransmission through the same glass ceramic body in the CIE Norm ValentSystem CIExyY: Limit curve G1 x Y 0.71 0.27 0.17 0.02 0.12 0.08 0.050.30 0.01 0.60 0.08 0.81 0.28 0.70 0.71 0.27.


5. The display device according to claim 4, wherein the glass ceramicpanel causes the standardized chromaticity coordinate of the lamp toappear on or above the limit curve (G2) which is determined by thefollowing coordinates in transmission through same glass ceramic body inthe CIE Norm Valent System CIExyY: Limit curve G2 x Y 0.64 0.28 0.200.07 0.17 0.09 0.10 0.30 0.08 0.56 0.12 0.70 0.26 0.65 0.64 0.28.


6. The display device according to claim 1, wherein light whosechromaticity coordinate is different from the original chromaticitycoordinate of the lamp is created on the display side formed by theglass ceramic front side.
 7. The display device according to claim 1,wherein light whose chromaticity coordinate is compensated from the sameoriginal chromaticity coordinate of the lamp is created on the displayside formed by the glass ceramic front side.
 8. The display deviceaccording to claim 1, wherein light whose chromaticity coordinate in theCIE Norm Valent System CIExyY is in or on the limit of the white range(W1) is created on the display side formed by the glass ceramic frontside, which is determined by the following coordinates: W1 x y 0.3 0.250.26 0.32 0.37 0.43 0.51 0.48 0.48 0.35 0.35 0.3.


9. The display device according to claim 8, wherein light whosechromaticity coordinate in the CIE Norm Valent System CIExyY is in or onthe limit of the white range (W2) is created on the display side formedby the glass ceramic front side, which is determined by the followingcoordinates: W2 x y 0.3068 0.3113 0.3028 0.3304 0.3205 0.3481 0.32070.3462 0.3376 0.3616 0.3551 0.376 0.3548 0.3736 0.3736 0.3874 0.40060.4044 0.3996 0.4015 0.4299 0.4165 0.4562 0.426 0.4813 0.4319 0.45930.3944 0.4147 0.3814 0.3889 0.369 0.3898 0.3716 0.367 0.3578 0.35120.3465 0.3515 0.3487 0.3366 0.3369 0.3222 0.3243 0.3221 0.3261.


10. The display device according to claim 1, wherein the white lamp is awhite LED or a fluorescent tube.
 11. The display device according toclaim 1, wherein the white lamp emits white light and the compensationfilter is designed so that colored light with a color saturation between0.99 and 0.5 is emitted on the glass ceramic front side.
 12. The displaydevice according to claim 1, wherein the compensation filter has abrightness value of greater than 10 for transmitting standard light E inthe CIExyY system (1931, 2° observer).
 13. The display device accordingto claim 12, wherein the brightness value is greater than
 40. 14. Thedisplay device according to claim 1, wherein the compensation filter isa color filter film.
 15. The display device according to claim 14,wherein the color filter film has a thermal stability in the range ofgreater than or equal to 80° C.
 16. The display device according toclaim 14, wherein the color filter film has a thermal stability in therange of greater than or equal to 150° C.
 17. The display deviceaccording to claim 14, wherein the color filter film has a mask.
 18. Thedisplay device according to claim 1, wherein the compensation filter isprinted on the glass ceramic panel.
 19. The display device according toclaim 1, wherein the glass ceramic panel has a thickness in the rangebetween 3 and 6 mm.